1. Field of the Invention
The present invention essentially relates to a chemical property sensor apparatus having a field effect transistor (FET) and, more particularly, to an FET sensor apparatus of a flow-cell adaptive type, and also to a method of manufacturing the FET sensor apparatus.
2. Description of the Related Art
Recently, sensors having an FET and designed to perform an electro-chemical analysis on various samples are being developed.
A prototype of such an FET sensor, known as an "ion-sensitive FET (ISFET) sensor," was first proposed by Piet Bergveld in 1972. The principles and operating characteristics of the ISFET sensor have already been determined.
Thereafter, Professor Matsuo at Tohoku University and some other persons invented practical ISFET sensors which have a multi-layered ISFET chiefly made of silicon nitride and which exhibit an improved sensitivity.
Further, U.S. Pat. No. 4,020,830 discloses an FET sensor which has an FET transducer. This FET sensor not only can detect pH degree and inorganic ions, but also can be used in analyzing chemical properties of glucose, urea, enzymes, immune substances, and the like, and can detect gas components such as O.sub.2 and CO.sub.2.
The FET sensors, thus far proposed and invented, are shaped like a stylus, mostly for two reasons. First, a sensor can easily be applied, if shaped like a stylus, to electro-chemical analysis of living things. Second, it can be manufactured easily if shaped like a stylus.
A stylus-shaped ISFET sensor is disclosed in, for example, Published Unexamined Japanese Patent Application No. 53-25385. This ISFET sensor is manufactured in the following way. First, a comb-shaped unit is made, each tooth of which is an ISFET. Then, the unit is cut into stylus-shaped pieces, i.e., ISFET sensors. This method is practical for mass-production of ISFET sensors.
In use, the stylus-shaped ISFET sensor, thus manufactured, is attached to a catheter, along with a reference electrode, thereby to measure the chemical properties of living tissues. Alternatively, it is immersed in a liquid sample to measure the chemical properties thereof.
To analyze sample blood, for example, a continuous analysis system of flow cell type is employed in most cases. Sensitive elements other than ISFETs, generally known as "ion-sensitive electrodes," are attached to the flow cells of this analysis system. Such an ion sensitive electrode is disclosed in Research Report, the Committee for Promoting Technical Development, Asahi Glass Kogyo Co. Ltd., Vol. 29, 1976, p. 227, FIG. 1(B).
The ion-sensitive elements can be replaced by ISFETs. However, it is very difficult to attach an ISFET to a flow cell since the ISFET is far smaller than an ion-sensitive electrode. Further, there is the risk that the sensitive membrane covering the tip of the ISFET may be broken when the ISFET is attached to the flow cell. Still further, the ISFET, once attached to the flow cell, protrudes therefrom and inevitably disturbs the liquid sample flowing in the flow cell, causing a turbulence in the liquid sample or forming bubbles in the liquid sample. As is known in the art, a turbulence or bubbles in a liquid sample results in incorrect measuring of the chemical properties of the liquid sample. In view of this, a full use cannot be made of an ISFET, though far smaller than an ion-sensitive electrode, when the ISFET is attached to a flow cell.